Change the precedence of fast pipe in the presence of function applic…

[anmonteiro]

…ation

[anmonteiro]

we need to processFastPipe of funExpr because we only processed applicationExpr in unparseExprRecurse and it may have bailed (e.g. if applicationExpr is an underscore application pattern).

[chenglou]

The be clear: this is a precedence change. It doesn't affect BS side, because x->y(z) was turned into x |. (y z) and then through the ppx, y x z. Now it'll be turned into (x |. y) z which through the ppx becomes (y x) z aka also y x z. Same perf, same type checking (?), same semantics when z is a argument (aka, x->y(~z) still works.

This change is only to accommodate non-bsb-native users who don't get the |. ppx transform (into which -> is desugared, and would still like to use it by redefining it themselves as an infix operator: let (|.) = (a, b) => b(a)*. This won't have the same perf benefits (there might be intermediate functions), doesn't work with labeled arguments and won't type check the same way. But at least it'll work.

* Before this diff, this wasn't possible, since we transform x->y(z) into x |. (y z), whereas they needed (x |. y) z.

cc @bobzhang @IwanKaramazow to confirm!